Method and control device for controlling the amount of fuel for an internal combustion engine

ABSTRACT

A control device for controlling the quantity of fuel which is supplied to the cylinders of an internal combustion engine by means of an injection device at each cylinder exhibits a precontrol timer 10, an individual-value memory 11 and a logic device 12. The individual-value memory stores individual values which are provided to the injection devices for the individual cylinders of an internal combustion engine 13. The logic device logically combines the individual values with a precontrol time provided by the precontrol timer, in such a manner that such a control time is obtained for each injection device that the lambda values individually measured for each cylinder by a lambda probe in the exhaust gas are essentially equal for all cylinders. It is possible to achieve very advantageous exhaust gas values with such a control device.

FIELD OF THE INVENTION

The invention relates to a method for controlling the quantity of fuelmetered individually to each cylinder of an internal combustion engineby means of an injection device, and a device for carrying out thismethod.

BACKGROUND OF THE INVENTION

A known control device exhibits a precontrol timer which outputsprecontrol times in dependence on rotational speed and quantity of airdrawn in with a particular precontrol time applying jointly to allinjection valves. A lambda control operating uniformly on all cylindersis superposed on the precontrol.

In the known control device it is a problem that variations incharacteristics of the different cylinders are not taken intoconsideration, which can lead to an individual cylinder of the internalcombustion engine delivering an exhaust gas which is relatively rich inpollutants. It has been attempted up till now to keep the cylindervariations small, particularly by designing the internal combustionengine in such a manner that very similar conditions prevail in all gaspaths.

A development of such a control device is disclosed in U.S. Pat. No.4,483,300.

This control device determines a pulse time, which is effectiveindividually for each cylinder, for metering fuel for each cylinderbased on variables which are the same for each cylinder. The controldevice also determines multiplicative correction factors which arespecific for each cylinder.

SUMMARY OF THE INVENTION

The invention is based on the object of providing a method and a controldevice of the type initially mentioned which has a compensating effectwith respect to cylinder variations. The invention is also based on theobject of providing a method for adjusting parameters of such a device.

The method according to the invention is characterized by the fact thatit compensates variations in the characteristics of the differentcylinders of an internal combustion engine by modifying the knownprecontrol by means of individual correction values which are formedfrom a combination of individual factors and individual summands. Thus,the injection devices are not all driven with the same injection timebut the precontrol time for each cylinder is corrected in such a mannerthat the exhaust gas from all individual cylinders essentially exhibitsthe same composition.

The method according to the invention is further characterized in that adetermination is made for which cylinder the lambda value measured inthe exhaust gas deviates from a predetermined value and then thecorrective value or values for this cylinder are changed until thepregiven lambda value results.

In order to store the individual correction values, the device accordingto the invention has an individual-value memory. A logic devicelogically combines the common precontrol time with the individualcorrection values.

If a lambda probe is used for the measurement which measures from therich to the lean range without jump characteristics, for example a probeof the pump current type with essentially linear characteristic, thereare relatively few problems in detecting deviations from lambda = 1 andsetting to lambda = 1. However, considerable complexity is required inprocessing the signal from the probe as such probes are relativelysensitive not only to fluctuations of the exhaust gas composition butalso to pressure fluctuations. Nernst-type probes present fewer problemswith respect to the latter. It is also recommended to use these probesbecause the probe frequently already installed in the vehicle, which, asa rule, is a Nernst-type probe, can then be used as measuring probe.When such a probe type is used, a method by successive approximation isproposed. In this method, the injection time is changed in such a mannerthat, for example, a distinctly lean exhaust gas should be achieved. Ifthis is not the case, this indicates a deviation of the characteristicsof the cylinder monitored from the characteristics of the othercylinders in the direction of a rich setting, to an extent which must becompensated in accordance with the change effected in the injectiontime. After this compensation, a change is carried out for achieving arich mixture. These alternating changes are repeated with lower andlower amplitude until a predetermined minimal amplitude is reached.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are explained in greater detail in thedescription following and are shown in the drawing, in which:

FIG. 1 shows a block diagram of a control device comprising anindividual-value memory and a logic device;

FIG. 2 shows a diagram for explaining the relationship between a loadvariable tL and the injection time ti;

FIG. 3 shows a block diagram of a control device comprising anindividual-value memory which stores individual factors and individualsummands, and a logic device which multiplies and adds; and,

FIG. 4 shows a block diagram of a control device and of a test devicewherein the control device has an individual-value memory withindividual factors which can be varied with the aid of the test device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The control device according to FIG. 1 has a precontrol timer 10, anindividual-value memory 11 and a logic device 12 which outputs correctedprecontrol times to injection devices (not shown) in an internalcombustion engine 13. The precontrol timer 10 is driven by means of asignal which is proportional to the rotational speed n, and aload-indicating signal which is identified with QL in FIG. 1,corresponding to a measured quantity of air per unit time. However, theload signal can also be determined, for example, by the intake pressureor the throttle flap position. Apart from these input variables,conventional precontrol timers frequently also take into considerationother quantities, particularly the engine temperature, but this is of noimportance to the explanations following. The logic device 12 logicallycombines precontrol times output by the precontrol timer 10 withcorrection values which are read out of the individual-value memory 11.These correction values are separately determined for each injectiondevice of the internal combustion engine 13 in such a manner that ineach case such a control time is obtained for each injection device thatthe lambda values measured individually for each cylinder by means of alambda probe in the exhaust gas are essentially equal for all cylinders.

Before discussing details of the invention in greater detail, FIG. 2will first be used to explain how cylinder variations can be generallycompensated for.

In FIG. 2, the relationship between the injection time ti for a singlecylinder and a load variable TL common to all cylinders is shown. Theload variable TL is obtained, for example, by dividing the air quantityWL per unit time by the rotational speed n and multiplying the result bya constant which adjusts the result of the division in such a mannerthat a time is obtained which is within the range of conventionalinjection times of a few milliseconds. The load variable tL is thus apreliminary injection time.

So that the exhaust gas from a single cylinder exhibits the same lambdavalue, for example lambda = 1, in all operating conditions, theinjection time ti must vary proportionally to the air quantity QL perunit time and inversely proportionally to the rotational speed n, thatis, overall, proportionally to the load variable tL. This is shown bythe dashed line in FIG. 2. The dashed line shows the followingrelationship:

    ti = az * tL,

where az is an individual factor which holds for the cylinder z. Thisfactor is only equal for all cylinders if all injection devices deliverexactly the same quantity of fuel within the same injection time and ifexactly the same quantity of air per unit time passes through allcylinders in each case. If, in contrast, one of the cylinders has aninjection device which delivers, for example, 5% less fuel per unit timethan the other injection devices, the factor az for the cylinder zhaving this injection device is to be selected higher by 5% than theindividual factors for the other cylinders. Correspondingly, it isnecessary to raise an individual factor by, for example, 5% if 5% moreair per unit time flows through one cylinder than through the othercylinders.

In the considerations listed above, it was assumed that all injectiondevices constantly deliver the same fuel quantity per unit time overtheir entire particular drive time. However, this is not the case inpractice since injection devices, for example injection valves, openmore slowly than they close. This fact must be taken into considerationby an additional time, an individual summand bz. This results in thefollowing relationship in accordance with the continuous straight linein FIG. 2:

    ti = az * tL + bz.

This equation, which holds true for each cylinder z contains twounknown, namely the individual factor az and the individual summand bz.In order to be able to determine these individual values, the values tiand tL must be determined for two points on the function line, namelyfor a lower and an upper point, preferably for idling and for full loadin the present case. This results in the following two equations:

    tiu = az * tLu + bz                                        (1)

    tio = az * tLo + bz                                        (2)

Subtracting equation (1) from equation (2) and evaluating with respectto az results in:

    az = (tio - tiu)/(tLu - tLo)                               (3)

The following is then obtained from equations (1) and (3) for theindividual summand bz:

    bz = tiu + tLu * (tio - tiu)/(tLu - tLo)                   (4)

The values thus obtained are stored in an individual-value memory whichis a part of the control device shown in FIG. 3 and is there identifiedwith 11.1. The control device also has a load variable transducer 10.1and a logic device 12.1. The load variable transducer 10.1 forms thequotient QL/n and also multiplies by a factor in such a manner that aload variable is obtained in the sense of a preliminary injection timeas explained above. This load variable is multiplicatively multiplied inthe logic device 12.1 with one individual factor a1, a2, a3 or a4 and acorresponding individual summand b1, b2, b3 or b4 is added by means of asumming element corresponding thereto. As a result, individual injectiontimes pass to corresponding ones of the injection devices at each of thecylinders of an internal combustion engine 13.

A simpler configuration of an individual-value memory and of a logicdevice is obtained if it is not intended to take into considerationvariations due to aging in the summand described. This results in aconfiguration which is a part of the block diagram of FIG. 4.

In the block diagram according to FIG. 4, a control device 14 and a testdevice 15 are present and both are indicated by framing with dot-dashedlines. Initially, only the control device 14 is of interest. This devicehas as control device a precontrol-time memory 10.2, an individual-valuememory 11.2 and a logic device 12.2. In the individual-value memory11.2, only individual factors f1, f2, f3 and f4 are stored. To obtainthese factors, it is no longer necessary to carry out two measurementsas explained above with reference to equations (3) and (4) but onemeasurement is sufficient, for example that according to equation (3),the summand bz being set to zero and a factor fz standing for the factoraz.

In the precontrol-time memory 10.2, precontrol times are addressablystored which can be addressed via values of the air quantity QL and therotational speed n and under certain circumstances, via furtheroperating variables (not shown). The logic device 12.2 multiplies aprecontrol time which is common to all cylinders by an individual factorf1, f2, f3 and f4 and supplies the thereby individualized control timesto the particular associated injection device in the internal combustionengine 13. If the precontrol times have been correctly determined forall operating conditions and there are no changes due to aging in thevariations of the above-mentioned summands bz, it is unimportant for theaccuracy of the correction that the summands in the control device arenot separately taken into consideration in the control device 14. It issufficient to determine the individual factors fz from time to time new.

Apart from the precontrol, the control device 14 according to FIG. 4also has a superposed control system. The control system is of nosignificance to the invention and will be described only briefly heresince it represents the usual design of control devices. Namely, anotherlambda probe 16 is arranged in the exhaust gas stream 17 of the internalcombustion engine 13. This probe has an actual lambda value which issubtracted from a desired lambda value. The desired value is read out ofa desired-value memory 18 which is addressable via the operatingvariables which were mentioned in the description of the precontrol-timememory 10.2. The control deviation thus formed is supplied to aregulating device 19 which outputs a correction factor KF, by means ofwhich the precontrol time read out of the precontrol-time memory 10.2 iscorrected by multiplication in such a manner that the control deviationshould disappear. Such a control superposed on the precontrol can beused not only with the embodiment of a control device according to FIG.4 but in conjunction with any arbitrary control device according to theinvention as in FIG. 1.

It has been mentioned above that the relationship shown in FIG. 2 onlyholds true if a particular lambda value is kept constant within theentire load range. In the text which follows, it is described on thebasis of FIG. 4 how the lambda value can be adjusted and how theindividual values can be determined.

The test device 15 according to FIG. 4 is used for carrying out themeasures just mentioned. This device is subdivided into three sections,namely a measuring section 15.1, a test section 15.2 and a programmingsection 15.3. The measuring section 15.1 has a display device 20 fordisplaying the lambda value measured in the exhaust gas stream 17. Inorder that this lambda value is no longer given to the subtractingelement for forming the control deviation for the regulating device 19but reaches the display device 20, the control device 14 has achange-over switch 21 which carries out an appropriate switch-overoperation following a switch-over signal US from the test device 15. Atthe same time, the output signal from the regulating device 19 isinterrupted and, instead, a constant correction factor KF = 1 formultiplying by precontrol times is outputted.

The test section 15.2 has a test factor adjusting device 22 and a testfactor multiplexer 23. Correspondingly, the programming section 15.3 hasan individual-factor adjusting device 24 and an individual-factormultiplexer 25. Each of four output lines of the multiplexer isconnected to a register in the individual-value memory 11.2 which storesa corresponding individual factor.

It is assumed that the lambda value is measured by means of a lambdaprobe having a linear output signal and that all adjusting processes areeffected manually.

Initially, all individual factors f1, f2, f3 and f4 in theindividual-value memory 11.2 are set to the initial value 1 via theindividual-factor multiplexer 25. Then the display device 20 is observedto see whether there is a deviation from lambda = 1. If such a deviationexists, for example in the direction of rich as shown in FIG. 4, a testfactor of 0.8 is individually supplied cylinder by cylinder to therelevant register in the individual-value memory 11.2 via the testfactor multiplexer 23. The content of the other registers is set to 1via the individual-factor multiplexer 25. Multiplying a precontrol valueby the value 0.8 leads to the lambda value being displaced in thedirection of lean. As soon as the register associated with the cylinderwhich triggered the deviation in the direction of rich on the displaydevice 20 is driven with the factor of 0.8, this deviation disappears.

After a deviating cylinder has been found in this manner, the individualfactor 1 is also established again for this cylinder. The lambda valuefor this cylinder, for example 0.95, is then measured on the displaydevice. Exactly this value is then adjusted from the outside asindividual factor in the individual-factor setting device 24 via asignal EIF and the individual-factor multiplexer 25 is driven by asignal NFM in such a manner that it writes the factor 0.95 in theindividual-value memory 11.2 exactly into the register responsible forthe cylinder found. This measure ensures that the cylinder concerned nolonger deviates in the direction of rich compared with the othercylinders.

Using a lambda probe having a linear characteristic has the advantagethat lambda values can be directly read off. However, an accurateindication is ensured only if signal disturbances caused by pressurefluctuations in the exhaust gas are compensated by measuring techniques,which is expensive. Previous probes having a linear measuringcharacteristic are very sensitive to such pressure fluctuations. Afurther disadvantage in the use of such probes is that it is notpossible to use an installed lambda probe directly since, in accordancewith the present state of the art, such a probe is usually a probe ofthe Nernst type with jump characteristics between the rich range and thelean range. The text following explains the method according to theinvention using such a probe, also on the basis of FIG. 4.

Initially, all individual factors are again set to 1 in theindividual-value memory 11.2 via the individual-factor multiplexer 25.Then a common test factor of 0.8, which should lead to a lean signal forall cylinders, is output via the test factor multiplexer 23. If this isthe case, a test factor of 1.2 is output. The consequence should be arich signal for all cylinder. If this is also the case, the test factoris changed to 0.85. If then a cylinder indicates a rich signal, thismeans that this cylinder is running in the direction of rich by 15% incomparison with the other cylinders. Which cylinder is triggering thesignal is determined by the fact that each cylinder is supplied in turnwith the test factor of 0.8 while the other cylinders still receive thefactor 0.85 as before. If the rich signal disappears, this is a sign ofthe fact that the cylinder which triggered the signal has just beendriven. The individual factor 0.85 is then set for this cylinder in theindividual-factor setting device 24. If the test factor is changed infurther steps, it is given to the associated register in theindividual-value memory 11.2, multiplied by the individual factor setfor the cylinder concerned.

The steps described are repeated until the test factors for rich andlean only exhibit a predetermined deviation of 1, for example 2%.

It is pointed out that the test factor, instead of being connected to adevice which performs a multiplicative combination with the individualfactor, could also be connected to the line for the correction factor KFwhich in any case leads to a logic device acting multiplicatively.

The two methods described are applicable not only to the control deviceaccording to FIG. 4 which only stores individual factors fz but also tothe embodiment of the control device according to FIG. 3, which storesindividual factors az and individual summands bz. The summands bz arethen set to zero in the individual value memory. Lambda = 1 is set bychanging the factors and the associated values of load signal andinjection time are measured. This is carried out for a lower and anupper load variable according to equations (3) and (4) whereupon arespective individual factor az and an individual summand bz can becalculated.

The methods have up to now been described for manual execution. Theprocess sequences show, however, that they can be automated withoutproblems. They can then be quickly and reliably carried out, for exampleduring the final assembly on a conveyor of an engine production line orduring customer service. The test device 15 can be constructed as aseparate device or can also be accommodated in the housing whichaccommodates the control device. In the latter case, the individualvalues can be set regularly, for example after a predetermined timeafter the internal combustion engine has been started. However, thisaffords no significant advantages since the largest variations arecompensated by setting during final assembly and variations due to agingonly occur over relatively long periods of time.

If the above method using the successive approximation is automated, itmust be monitored, as described, whether an error signal in thedirection of rich occurs when actually only lean signals are expectedand conversely. If it is now to be observed whether this signaldisappears cylinder by cylinder during the changing of test factors, itcan happen that the signal is maintained, namely if it is not only asingle cylinder which exhibits a variation in the wrong directionobserved, but if this is the case with two or even more adjacentcylinders. If this is found, the test factors must be jointly changed inthe manner described for two adjacent cylinders and if a signal remainseven then, for three adjacent cylinders and so forth. Instead, it isalso possible to monitor, in addition to the amplitude, also the timeduration of the error signal. If two adjacent cylinders exhibit thevariation error the signal amplitude is maintained duringtesting-through but for only half the time as during the pre-testmeasurement for finding the cylinder with variation. A cylinder is thenidentified by observing signal amplitude and signal duration as in themanual setting.

As explained, it is possible to determine individual values in such amanner that such a control time is obtained for each injection device,that the lambda values individually measured for each cylinder by alambda probe in the exhaust gas are essentially equal for all cylinders.If these values are stored in the individual-value memory of a controldevice and logically combined with a common precontrol time by means ofa logic device, all cylinders essentially supply an exhaust gas havingthe same lambda value. This makes it possible to reduce the pollutantcontent for all cylinders uniformly. It is then no longer necessary, asbefore, for some cylinders to have to run slightly too richly and theother ones slightly too leanly only in order to obtain a satisfactorymean value.

It is pointed out that the value of the summands bz depends on thevoltage with which the injection devices are driven. If a non-regulatedvoltage is used for this, which can thus fluctuate, each summand bz mustbe corrected, which is effected most suitably by multiplying it by aquantity which is proportional to the drive voltage for the injectiondevices.

The individual-value memory in all embodiments is most suitablyconstructed as PROM and, in particular, as EEPROM. If then a method fordetermining individual correction values is carried out in a customerservice, the newly determined values can be written into the EEPROM. Itis also possible to use a non-volatile RAM but a control device whichcontains a control device of the type described must then also contain atest device which makes it possible to automatically determine newindividual correction values whenever an initialization process formemories has become necessary, and to write these correction values backinto the RAM.

All memories and devices described are advantageously given by sectionsand functions of a microcomputer such as is widely used today in engineelectronics.

I claim:
 1. A method of controlling the quantity of fuel which ismetered to the individual cylinders of an internal combustion engine bymeans of an injection device, the method comprising the stepsof:correcting precontrol times, which are common to all cylinders anddependent on rotational speed and air quantity drawn in by suction, withindividual corrective values dependent upon lambda actual values;forming the individual corrective values from a combination ofindividual factors (az) and individual summands (bz); determining thecylinder for which there is a deviation of the airfuel ratio from apregiven lambda value in the event of a deviation of the value, which ismeasured by the lambda probe, from a pregiven lambda value; adjustingthe desired lambda value by changing the individual factors (az);determining the value of the injection time (tiu) corrected as may berequired and belonging to the desired lambda value at (tLu); adjustingthe desired lambda value by changing the individual factors after anupper value (tLo) of the load variable occurs and in the event of adeviation of the value measured by the lambda probe from a pregivenvalue; determining the value of the injection time (tio) corrected asmay be required and belonging to the desired lambda value (tLo);computing and storing the individual factor (az) and the individualsummand (bz) for a specific cylinder from the equations:

    tiu = az x tLu + bz

    tio = az x tLo + bz

and, again examining the computed values for (az) and (bz) andcorrecting said values (az) and (bz) as may be required after theoccurrence of the value (tLu) of the load variable.
 2. The method ofclaim 1, wherein the method of determining for which cylinder theair/fuel mixture deviates from a pregiven lambda value is performed withthe further steps of:changing the injection time of all cylinders in thedirection acting opposite to the observed deviation with each cylinderbeing taken in turn; and, observing at which cylinder the injection timehas just been changed when a reduction of the deviation or a reversalthereof has occurred in the opposite direction.
 3. The method of claim1, wherein the individual factors are changed so that a lambda value ofas close to one as possible is obtained when a lambda probe is usedwhich measures from the rich into the lean range without a jumpperformance, the method comprising the further steps of:measuring thelambda value; and, multiplying that individual factor on the basis ofwhich the lambda measurement occurred by the measured lambda value. 4.Method of claim 3, wherein: when a lambda probe is used which exhibitsjump characteristics on transition from the rich to the lean range, theindividual factors are varied in such a manner that a lambda value of asaccurately as possible one is achieved, by means of the steps below:(a)a test factor TF having such a magnitude that a strong lean lambda valueshould occur, for example TF = 0.8, is superposed on the individualfactor for the cylinder (z) for obtaining an injection time for theinjection arrangement at the cylinder (z),(a1) if this is so, passing tostep b, (a2) if this is not so, the individual factor is multiplied bythe test factor for obtaining a now applicable individual factor and themethod is continued as follows: (b) a test factor TF of such a magnitudethat a strong rich lambda value should occur, for example TF= 1.2, ismultiplicatively superposed on the individual factor,(b1) if this is so,passing to step c, (b2) if this is not so, the individual factor ismultiplied by the test factor for obtaining a now applicable individualfactor, and the method is continued as follows: (c) the magnitude of thetest factor for the next lean step is varied compared with the magnitudeof the test factor in the preceding lean step, in such a manner that itis closer to one,(c1) if the test factor TF now applicable is greaterthan or equal to a lean limit value, for example TF = 0.98, passing tostep d, (c2) if the test factor now applicable is smaller than the leanlimit value, terminating the method, (d) the test factor ismultiplicatively superposed on the individual factor, which shouldresult in a lean lambda value, (d1) if this is so, passing to step e,(d2) if this is not so, the individual factor is multiplied by the testfactor for obtaining a now applicable individual factor and the methodis continued as follows: (e) the magnitude of the test factor for thenext rich step is varied compared with the magnitude of the test factorin the preceding rich step in such a manner that it is closer toone,(e1) if the new test factor TF is less than or equal to a rich limitvalue, for example TF = 1.02, passing to step f, (e2) if the new testfactor is greater, that is closer to one than the rich limit value,terminating the method, (f) the test factor is multiplicativelysuperposed on the individual factor, as a result of which a rich lambdavalue should occur, (f1) if this is so, passing to step c, (f2) if thisis not so, the individual factor is multiplied by the test factor forobtaining a now applicable individual factor and the method is continuedat step c.
 5. A control apparatus for controlling the quantity of fuelwhich is metered to the individual cylinders of an internal combustionengine with an injection device which meters the desired quantity offuel to each cylinder, the apparatus comprising:precontrol timetransducer means for supplying the precontrol times (TL) in dependenceupon rotational speed and the air quantity drawn in by suction with theparticular precontrol time applying in common for all injection valves;individual valve memory means for storing corrective values for allcylinders individually; a logic device for logically combining thecommon precontrol time with individual corrective values dependent uponlambda actual values; means for adjusting a lower value (tLu); means fordetermining a deviation of the value measured by the lambda probe from apregiven lambda value and for detecting for which cylinder theair/fuel-ratio deviates from the pregiven lambda value; means foradjusting the desired lambda value by changing the individual factor(az); means for determining the injection time (tiu) belonging to thelower load variable (tLu) at the desired lambda value; means foradjusting an upper value (tLo) of the load variable and for adjustingthe desired lambda value by changing the individual factor in the caseof a deviation of the value measured by the lambda probe from a pregivenlambda value; means for determining the injection time (tio)corresponding to the upper load variable (tLo) at the desired lambdavalue; means for specifying and storing the individual factors (az) andindividual summands (bz), which are dependent on the lambda actualvalues, in accordance with the equations:

    tiu = az x tLu + bz

    tio = az x tLo + bz

means for again examining the computed values of (az) and (bz) after arenewed adjustment of the value (tLu) of the load variable and forcorrecting the computed values of (az) and (bz) as may be required. 6.The control apparatus of claim 5, further comprising:a regulating device19 which outputs an actuating signal which is superposed on theprecontrol times; and, a switch-over device 21 for switching betweenregulating operation and setting operation, the actuating signal beingswitched off in the setting operation and a method for determining theindividual correction values is carried out.
 7. The control apparatus ofclaim 6, wherein said precontrol time transducer is a precontrol-timememory 10.2 for storing precontrol times for lambda values = 1,addressable via values of addressing operating variables which includethe rotational speed and an operating variable which indicates thequantity of air drawn in; the individual-value memory 11.2 stores anindividual factor (fz) for each cylinder (z); and, the logic device 12.2multiplies the particular precontrol time for each injection valve,which is common to all injection valves, by the individual factorallocated to the associated cylinder.
 8. The control apparatus of claim6, wherein said precontrol-time memory means is a load variabletransducer 10.1 which outputs a load variable QL/n which is proportionalto the quotient of air quantity per unit time divided by revolutions perunit time; individual-value memory means 11.1 store an individual factor(az) and an individual summand (bz) for each cylinder (z); and, thelogic device 12.1 multiplies the particular load variable for eachinjection device, which is common to all injection devices, by theindividual factor (az) allocated to the associated cylinder and adds theassociated individual summand (bz).